字符串做异或使用union

#include <stdio.h>
#include <sys/time.h>
#include <string.h>

union data
{
    unsigned char str[];
    unsigned long long ll_value[];
    unsigned int i_value[];
};

int main(int argc, char **argv)
{
    union data a;
    union data b;
    struct timeval start, end;
    int i = ;

    memset((char *)&a, , );
    memset((char *)&b, , );

    gettimeofday(&start, NULL);
    for (i = ; i < ; i++)
    {
        a.str[i] = a.str[i] ^ b.str[i];
    }
    gettimeofday(&end, NULL);
    printf("take %dus \n", (int)(((end.tv_sec-start.tv_sec)*+end.tv_usec)-start.tv_usec));

    gettimeofday(&start, NULL);
    for (i = ; i < ; i++)
    {
        a.ll_value[i] = a.ll_value[i] ^ b.ll_value[i];
    }
    gettimeofday(&end, NULL);
    printf("take %dus \n", (int)(((end.tv_sec-start.tv_sec)*+end.tv_usec)-start.tv_usec));

    gettimeofday(&start, NULL);
    for (i = ; i < ; i++)
    {
        a.i_value[i] = a.i_value[i] ^ b.i_value[i];
    }
    gettimeofday(&end, NULL);
    printf("take %dus \n", (int)(((end.tv_sec-start.tv_sec)*+end.tv_usec)-start.tv_usec));

　　return 0;
}

take 21us
take 3us
take 5us